New International Standards in Polymer Mass Spectrometry____________
Unit 1. History of metrology Measurements play an important role in man’s life. They turn up everywhere in his activities-from estimating a distance by eye to elaborate process control and scientific research.
The need to measure goes back to ancient times. Even then man had to measure distances, areas, dimensions, weights, time, and so on. At first, he used primitive measurements, done often by eye. It was customary for man to compare the objects of interest with, say, some parts of his body. Thus, the body’s parts served as standards, that is reference samples, with which man established units for various quantities. Obviously, both the standards and the unites were arbitrary, and this made a comparison of results difficult. With time, however, man realized the value of standards. Thus, the water clock was used as a standard reproducing a time interval. Later, “natural” standards came into practice. One example is the planet Earth itself –its period of rotation was used to reproduce the unites of time.
As human society developed, it relied increasingly more on commerce and sea-faring, built industry, and gave impetus to science. All this spurred the search for special technical facilities-instruments with which to measure various quantities.
Electrical measuring instruments appeared in the wake of early studies of electricity.
The world’s first electrical measuring instrument was built by G.V. Richman in 1745. It was the electrometer-an instrument designed to measure potential difference and intended for use in studies of atmospheric electricity.
In 1820, A. Ampere demonstrated the first galvanometer. It was essentially a magnetic needle acted upon by the field set up by a conductor carrying the current being measured. In 1837, Au. De la Rive invented a hot –wire electrical measuring instrument.
The latter half of the 19th century saw the emergence of electrical engineering-a division of science and technology concerned with practical uses of electricity (for communication, power generation, and the like). This explains why so much effort was put into a variety of electrical measuring instruments at the time.
In 1867, W. Thomson proposed a galvanometer which used a moving coil and a fixed electromagnet. In 1880-1881, M. Depres and J.A. d’Arsonval improved the galvanometer through the use of a permanent magnet. In 1881, F. Uppenborn invented a moving-iron instrument. At about the same time, M. O. Dolivo-Dobrovolsky, a Russian electrician who did much to advance electrical measurements, invented an induction wattmeter, an induction phase meter, and an iron-cored electrodynamic wattmeter, and laid down scientific recommendations for the design of iron-cored electrodynamic instruments in general. He also proposed new methods for measuring electric and magnetic quantities (notably, losses occurring in ferro-magnetic materials as they undergo reversals of magnetization). In 1872, A.G. Stoletov of Russia, while investigating how the permeability of iron was affected by magnetic field intensity, developed a technique to measure induction with a ballistic galvanometer. Towards the end of the 19th century, a light-beam oscillograph was developed to record electrical signals.
Although instruments were widely used as early as the 19th century, a single system of unites was non-existing, and the results of measurements carried out by different experimenters using different instruments were difficult to compare. This obviously stood in the way of further progress in science and technology. Aware of this limitation, some scientists made attempts to introduce a generally accepted system of units.
The problem was not solved, however, until the First Congress of Electricity held in 1881 adopted the first system of units.
Some countries set up metrological offices for the purpose of reproduction, maintenance and transfer of units of quantities with the aid of specially designed and fabricated reference samples, or standards.
Memorise the following words and word combinations:
a hot –wire electrical measuring instrument – тепловой электроизмерительный прибор; moving coil – подвижная катушка; a permanent magnet – неподвижный электромагнит; moving-iron instrument – электромагнитный прибор; induction wattmeter – индукционный ваттметр; an iron-cored electrodynamic wattmeter – ферродинимический ваттметр; reversals of magnetization - перемагничивание; permeability of iron – магнитная проницаемость железа; magnetic field intensity –напряженность магнитного поля; a light-beam oscillograph – светолучевой осциллограф; a single system of unites – единая система единицю
Find the Russian equivalents to the following word combinations:
came into practice; to reproduce; intended for use in studies; elaborate; technical facilities; standard; estimating a distance by eye; goes back to ancient times; arbitrary; magnetic needle acted upon the field; sea-faring; emergence of electrical engineering.
определение расстояний на глаз; сложный; возникла в древние времена; мера; произвольный; возникновение электротехники; магнитная стрелка на которую действует поле; воспроизводить; стали вводить в практику; технические средства; мореходство; предназначенный для изучения.
Translate into English using the active vocabulary of the lesson:
1) C измерениями человек встречается на каждом шагу своей деятельности начиная от определения расстояний на глаз и заканчивая контролем сложных технологических процессов и выполнением научных исследований.
2) В связи с изучением явлений электричества стали создаваться электроизмерительные приборы.
3) Вторая половина XIX в. ознаменовалась возникновением электротехники – области науки и техники, связанной с использованием явлений электричества 4) Он предложил метод измерения потерь в ферромагнитных материалах при их перемагничивании.
5) Для регистрации электрических сигналов в конце XIX столетия был разработан светолучевой осциллограф.
Translate at sight
Measuring and testing installations used in semiconductor technology measure various electrical quantities: current, voltage, resistance, capacitance, etc.
Most generally employed in semiconductor technology are instruments measuring the current intensity and voltage.
With measuring circuits, other electrical quantities (e.g., resistance, capacitance, and quality factors) are obtained from the measured values of the current or voltage or both.
To measure the current use is made of ammeters, milliammeters, and microammeters. for d.c. measurements, permanent magnet-moving coil (PMMC) instruments are most often used; for a.c. measurements, detecting and moving-iron instruments.
Voltage is measured by voltmeters and millivoltmeters of the PMMC, detecting, and moving-iron type.
Review the article “History of metrology”.
Forms and Methods of Measurements Measurements as experimental procedures by which one finds the value of the unknown are many and diverse. According to the way in which experimental data are processed in order to find the results, all measurements may be classed into direct, indirect, simultaneous, and cumulative.
A direct measurement is that which yielded the sought value of the measurand directly from experimental data obtained by the measurement process. An example is the measurement of voltages with a voltmeter.
An indirect measurement is that in which the value of a quantity is found from a known relation between this quantity and some other quantities for which the value can be found by direct measurements. In this case, the value of the measurand is found by solving the following equation:
X=(xэ, x2, x3, …, xn)
where xэ, x2, x3, …, xn are the quantities that lend themselves to direct measurements.
An example of indirect measurements is this: the resistance of a resistor is found from the equation
in which V is the voltage across the resistor and I is the current flowing through it. Both the voltage and the current can be measured directly.
A simultaneous measurement is that in which one simultaneously measures several distinct quantities connected by a relation of some form. This involves solving the following set of simultaneous equations: F(xэ, x 2, x3, …, xn, x′э, x′2, x′3, …, x′m)=0
xэ, x 2, x3, …, xn, =values of the sought quantities
x′э, x′2, x′3, …, x′m =values of the
x′′э, x′′2, x′′3, …, x′′m measured
xⁿэ, xⁿ2, xⁿ3, …, xⁿm quantities
An example of a simultaneous measurement is this: we wish to determine the manner in which the resistance of a resistor varies with temperature:
For this purpose, we measure the resistance of the resistor at three distinct temperatures, write a set of three simultaneous equations, and solve them for the parameters Ro, A and B.
A cumulative measurement is that in which one measures simultaneously several identical quantities, and the sought values are found by solving a set of equations written on the basis of the results which are obtained from direct measurements of various combinations of these quantities.
An example of a cumulative measurement is this: we wish to determine the total resistance of resistors connected in a delta. For this we first measure the resistance between each pair of the delta’s corner. This yields three results, and from them we find the unknown total resistance.
Measurements may be static or dynamic, depending on the state of the measurement devices used.
Static measurements are those in which the measurement device is operating in a static (or steady) state and its output signal, say, the deflection of the pointer, remains unchanged for the duration of the observation. Dynamic measurements are those in which the measurement device is operating in a dynamic (unsteady) state and its output signal is changing with time so much that the change must be taken into consideration when finding the final result. In order to assess the accuracy of a dynamic measurement, it is necessary to know the dynamic behaviour of the measurement device involved.
When the experimenter is interested in how a given quantity varies with time, he determines a series of consecutive values of this time-varying quantity. This involves a series of consecutive observations, each yielding an instantaneous value, that is, a value which exists at each instant. If, within the specified time interval, the measurand can take on a finite number of instantaneous values, we have a discrete measurement. If this number is infinite, we have an analog measurement. Methods of measurement
The numerical value of the unknown quantity is found by comparing it with another quantity of the same kind chosen as a unit and reproduced in a particular type of measurement device, called a standard.
According to the manner in which standards are used, the following methods may be defined: the direct evaluation method and the comparison methods.
In the direct evaluation method, the value of the unknown is determined directly from the indicating device of a direct-conversion instrument whose scale has been calibrated against a multi-valued standard reproducing values of the unknown. Which direct-conversion instruments, the operator compares the position of the pointer with the marking on the scale and reads the indication. An example of the direct-evaluation method is measurement of current with an ammeter.
In the comparison methods, as their name implies, the operator compares the unknown quantity with standard that reproduces another quantity of the same kind chosen as a unit. A major distinction of the comparison methods is that a known quantity takes part in the measurement process directly.
The comparison methods may further be divided into the null (or balance) method, the differential method, the substitution method, and the coincidence method.
Memorise the following words and combinations:
direct - прямой; indirect - косвенный; simultaneous - совместный; cumulative - совокупный; static - статическое; dynamic - динамическое; measurement devices – средства измерений; output signal –выходной сигнал; deflection of the pointer – отклонение указателя; finite – конечный; a discrete measurement – дискретное измерение; an analog measurement – аналоговое измерение; the direct evaluation method –метод непосредственной оценки; the comparison methods – метод сравнения; a direct-conversion instrument – измерительный прибор прямого преобразования; to calibrate - градуировать; a multi-valued standard – многозначная мера; null (or balance) method – нулевой метод; the differential method – дифференциальный метод; the substitution method – метод замещения; the coincidence method – метод совпадения